The invention relates to a rim for a cycle wheel. The invention is also aimed at a mounted assembly for cycles, more particularly for bicycles, consisting of a rim and of a tire. The invention is aimed more particularly at cycles intended to be associated with tires which are to operate without an inner tube, of the tubeless type.
An ordinary rim, made of a single part, of the tubeless type, in particular intended for motor vehicles, consists of different regions; first of all, starting from an outer edge of the rim, there is a rim flange, or flange, the main role of which is to retain the bead of the tire in the inflated state; next, the bead seat, on which the bead of the tire rests and which ensures the gripping thereof, as well as the airtightness; and finally, a groove intended to permit the mounting of the tire owing to the fact that its diameter is less than that of the flange. In the case of a rim having humps, the latter are present between the bead seat and the groove which allows the mounting. The humps are bosses, the function of which is to prevent or at the very least delay the occurrence of an unseating of the tire particularly in the event of a low pressure.
The usual procedure for mounting a tubeless tire on such a rim consists of various steps, as follows; firstly, a part of the first bead is passed over the rim flange and this part is placed in the groove. Then, the rest of the bead can be passed over the rim thanks to a slight ovalisation of the corresponding bead wire of the tire. The procedure is the same for passing the second bead over the rim flange. The mounting is then completed with a final step of inflation to a pressure which ensures that the beads are put in place on the seats, bearing on the rim flanges. During this last step, the beads pass over the humps which form an obstacle to the passage of the said beads as far as their respective seat.
Bicycle tires have some distinctive features; the bead wires are very flexible and the deformation of the lower region can thus be very substantial. This is not without its disadvantages in the case of a tubeless tire, since there must be complete tightness between the rim and the tire and more precisely between the rim and the beads of the tire.
Although not limited to such applications, the invention will be more particularly described with reference to mounted assemblies intended to equip bicycles for road use. A distinctive feature of these mounted assemblies is that the operating pressure is of the order of 8 bars; the latter possibly also attaining values of the order of 11 bars when the tires are subjected to extreme conditions, in particular in competition, during which the temperature of the air inside the tire may increase very substantially, and bring about an increase in the pressure. This is the case, for example, when braking heavily on mountain descents where the friction of the brake block on the rim leads to such a temperature increase.
It is known at present to produce mounted assemblies of the tubeless type for bicycles of the MTB (mountain bike) type; the operating pressure of such tires is of the order of 2 bars. There has already been described, in the patent application EP 0 893 280, an improved rim which facilitates the inflation conditions of such a tubeless tire and which improves the stability of the tire in the inflated state in the event of a violent lateral impact. Such a rim is characterized by the presence, on the one hand, of a narrow groove which promotes the inflation phase while ensuring the tightness between the beads and the rim; and, on the other hand, this rim is characterized by the presence at the groove edge of humps which allow the beads of the tire to be maintained on the seats provided for this purpose in the event of a violent lateral impact, in particular, for example, in the event of impact with stones.
Tests have been carried out with this type of rim for the production of a mounted assembly intended for road use and thus brought to pressures of the order of 8 bars. It turns out that, although in fact the use of a rim such as that described by the patent application EP 0 893 280 makes it possible to start the inflation of the tire with certainty, whatever the characteristics of the tires tested, above a certain pressure unseating of at least one bead occurs and consequently the tire comes off the rim. In addition, the pressures attained upon the unseating of the beads of the tire are generally less than 8 bars and thus less than the operating pressure commonly required and markedly less than the pressures which may be attained in extreme situations such as that set out above.
The inventors have thus set themselves the task of producing a rim, and a mounted assembly consisting of the said rim and of a tire, for use on bicycles for road use, the said mounted assembly being of the tubeless type and not presenting any risks to the user, in particular of coming off the rim, at the pressures normally required for this type of use.